Glass fibers are broadly used in the electronics field because of their excellent thermal resistance, dimensional stability, electrical characteristics and the like, and in particular, glass woven fabrics prepared by subjecting glass fibers to weaving are much in demand as a base material for a printed wiring board because of their excellent characteristics.
Such a packaging system is now increasing that IC or the like is automatically inserted into a printed wiring board. This automatic insertion is accompanied by drying of solder resist, heating such as fusing or the like, etc, and hence, the printed wiring board becomes exposed to severe conditions. Therefore, that the printed wiring board is changed in dimension by heat has become a problem. Particularly, when the dimensional change in the warp direction and that in the weft direction are different, it follows that anisotropy is caused in the warp and weft directions in the step of processing the printed wiring board.
Thus, the dimensional stability level in the conventional printed wiring boards has become unsatisfactory, and a printed wiring board free from anisotropy as to dimensional change has become necessary.
Moreover, in the case of conventional glass woven fabrics prepared by plain weave, fine irregularities resulting from the weave pattern of the woven fabric appear on the surface of the base board. As in recent years, the wiring of the printed wiring board has been made finer and the wiring density has been made higher, and therefore, it has been necessary that the irregularities be as small in number as possible.
In order to solve such problems, a printed wiring board has been proposed in which a unidirectionally arranged woven fabric of glass fibers (referred to herein-after as the UD material) is used as a base material. For example, JP-A-1-216,829, JP-A-1-216,830, JP-A-4-270,657, JP-B-7-90,606, JP-B-7-90,607, JP-A-8-39,686 and the like disclose a process and apparatus for producing a printed wiring board in which the UD material is used.
The production of a printed wiring board in which the UD material is used as a base material is characterized in that the printed wiring board can be produced without undergoing the conventional weaving step, varnish-impregnating step and pressing step, but there must be prepared its own peculiar production devices such as a yarn-arranging device and a continuously resin-coating device, and hence, a new investment in plant and equipment is required. Moreover, the above production has many undissolved technical problems and has not reached a practical use stage.
Furthermore, in recent years, a remarkable advance has been seen with respect to a technique of perforating the printed wiring board with a laser. However, when a printed wiring board in which a glass woven fabric is used as the base material is subjected to laser processing, such a problem is caused in some cases that holes having a uniform diameter cannot be perforated because in the conventional glass woven fabric of plain weave, present are portions in which fibers are woven with one another and portions of resin alone.
Accordingly, an object of this invention is to provide a glass woven fabric having characteristics equivalent to conventional unidirectionally arranged woven fabrics (the UD material), and to thereby make it possible to obtain a printed wiring board excellent in dimensional stability and surface smoothness by the conventional process, as it is, for producing a printed wiring board which is now generally used.
Another object is to provide a printed wiring board which enables the uniform perforation when the printed wiring board is subjected to perforation with a laser.